Business Segment (Sales by Major Product Line) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer
Net Sales	$ 626,969	$ 536,377
Rail Products
Revenue from External Customer
Net Sales	188,590	155,870
Rail Technologies
Revenue from External Customer
Net Sales	130,934	100,257
Piling and Fabricated Bridges Products
Revenue from External Customer
Net Sales	102,246	105,924
Protective Coating and Measurement Systems
Revenue from External Customer
Net Sales	89,026	67,766
Test , Inspection and Threading Services
Revenue from External Customer
Net Sales	59,766	50,683
Precast Concrete Products
Revenue from External Customer
Net Sales	$ 56,407	$ 55,877